Cooler for use in vapor jet diffusion pumps



May 12, 19 N. WARMOLTZ ETAL COOLER FOR USE IN VAPOR JET DIFFUSION PUMPSFiled April 4, 1955 INVENTOR NICOLAAS WARMOLTZ HENDRIK RUGT GERHARDCASIM BY M AGENT United COOLER FOR USE IN VAPOR JET DIFFUSION PUMPSNicolaas Warmoltz and Hendrik Brugt Gerhard Casimir,

Eindhoven, Netherlands, assignors, by mesne assignnients, to NorthAmerican Philips Company, Inc., New York, N.Y., a corporation ofDelaware Mercury vapor difiusion pumps are often provided with a coolerarranged between the pump and the space to be evacuated. These coolersare intended to collect the mercury vapor and any other vapors, forexample water vapor, contained in the duct between the pump and thespace to be evacuated and thus to prevent the mercury from entering thisspace to be evacuated. Otherwise the vapor pressure of the mercury vaporwould affect adversely the high vacuum in the space to be evacuated.

It is common practice to cool these coolers by means of liquid air orsolid carbonic acid, so that the cooler assumes a temperature lower than40 C. However, the use of these cooling agents is, in practice, attendedwith difiiculties, since at this low temperature the mercury vaporsublimates on the cooler. If the pump has been in operation for sometime, for example a few days, such a quantity of mercury vapor hassublirnated on the cooler, that owing to lack of liquid mercury the pumpcan no longer operate satisfactorily. It is then necessary to stop theevacuation of the space and to heat the cooler, so that the mercury canagain be supplied to the pump. Even with pumps operating by means of adifferent liquid, for example with certain oil diffusion pumps, the sameeffect is liable to occur under certain conditions.

The invention has for its object to construct the cooler in a mannersuch that the aforesaid adverse effect of sublimation cannot occur.

According to the invention the cooler is provided with a cooling plate,which is arranged in the path of the gas particles and provided withmeans, with the aid of which the temperature of the plate is maintainedso high that the vapor of the pump liquid near this cooling plate canonly condense thereon. It is desirable for the liquid produced on thecooling plate to have a viscosity such that, at the temperature of theplate, it drips readily off.

The means to maintain the desired temperature of the cooling plate,which temperature is about -30 C. for mercury, may be constructed invarious Ways.

In one embodiment of the invention the cooling plate is secured to thecooler by means of a heat conducting element, the thermal conductivityof which is such that the cooling plate is kept at the desiredtemperature. The thermal conductivity of the heat transferring element,which will frequently be shaped in the form of a rod, varies with thethermal conductivity coefiicient of the material of the rod and with thedimensions thereof.

In a further embodiment of the invention the cooling plate is secured tothe cooler by means of a heat transferring element and provided with aheating device in a manner such that it is kept at the desiredtemperature. The heating device will preferably be an electric heatingelement. This element is capable of supplying such a quantity of heat tothe cooling plate that it assumes the desired temperature.

ates Patent "ice The cooler and the cooling plate are preferablyarranged in a manner such that, in accordance with a further aspect ofthe invention, mercury vapor condensed on the cooling plate isimmediately resupplied to the pump, although, of course, it is alsopossible to collect the condensed mercury vapor for a comparatively longtime and to conduct it away periodically to the pump.

The invention will be explained more fully with reference to twoembodiments. I

Fig. 1 shows diagrammatically a system comprising a cooler, in whichbetween the cooling plate and the cooler provision is made of an elementhaving the desired heat conductivity, and

N Fig. 2 shows a cooler, in which the cooling plate is kept at thedesired temperatureby means of an electric heating helix.

In the system shown in Fig. 1 a vapor-jet diffusion pump, for example, amercury vapor diffusion pump is designated by 1. This pump may beconstructed in known manner. The pump co-operates with a pre-vacuumpump, which is not shown in the figure and which communicates with thepump through the duct 2; this prevacuum pump may for example be an oildiffusion pump or a rotating pump.

The mercury vapor diffusion pump communicates through a duct 3 with areceptacle 4, which surrounds a cooler 5. This cooler is filled througha filling aperture 6 with liquid air of 1 atmosphere and therefore has atemperature of about l95 C. To the cooler 5 is secured through a heattransferring element 7 a cooling plate 8. The element 7, as well as thecooling plate 8, may be made for example of corrosion-free steel and hasa size such that the temperature of the cooling plate may be for example-30 C. The surroundings and the condensing vapor transfer heat to thecooling plate 8; this heat is conducted away to the cooler 5. The space4 communicates through a duct 9 with a space 10, to be evacuated. If inthe duct 3 and in the space 4 below the cooling plate 8, located in thepath of the gas particles, mercury vapor would be present, this mercuryvapor will condense on the cooling plate 8 and it will not sublimate.The condensate produced will flow back into the pump 1, so that theactive quantity of mercury of the pump remains constant as much aspossible and it will not be necessary at all or be required only a fewtimes to stop the evacuation of the space in order to remove thesublimated mercury.

In the construction shown in Fig. 2 parts corresponding to those shownin Fig. l are designated by corresponding reference numerals. In thisconstruction a heat transferring element 11 is provided between thecooling plate 8 and the cooler 5. The heat transferring element issurrounded by an electric heating helix 12, so that heat can be suppliedto the cooling plate. However, if no additional measures are taken thetemperature of the cooling plate would be for example l C., if thecooler is filled with liquid air, owing to the high thermal conductivityof this element. Owing to the supply of heat by means of the heatinghelix, the cooling plate can assume the desired temperature. The cooleraccording to the invention may frequently be used, if the vapor jetdiffusion pump is driven by means of a different pump liquid.

What is claimed is:

1. In a vapor-jet diffusion pump for evacuating a container, a cooler, acooling member positioned between said pump and said container to beevacuated and adapted to transfer the heat in said container to saidcooler and located in the path of the vapor molecules, and a heattransferring element connecting said cooling member and said cooler, thethermal conductivity of said heat trans- 3 ferring element being of avalue whereby the temperature of said cooling member is maintained at apredetermined level higher than said cooler and such that the vapor ofthe pump liquid contacting said member condenses thereon.

2. In a vapor-jet diffusion pump for evacuating a container, a coolerpositioned between said pump and said container to be evacuated, acooling member located in the path of the vapor molecules and arrangedso as to shield said cooler from initial contact with the vapor issuingfrom said pump, and a heat transferring element connecting said coolingmember to the cooler, the thermal conductivity of said element beingsuch that the cooling member is kept at a predetermined temperaturelevel which is higher than the cooler and the vapor of the pump liquidcontacting said cooling member condenses thereon.

3. A vapor diffusion pump as claimed in claim 2 further comprising areceptacle containing said cooler, heat transferring element and coolingmember, a duct connecting said pump and receptacle, said cooling memberhaving a cone shaped surface with its apex directed toward said duct.

4. In a vapor-jet diffusion pump for evacuating a'container, a cooler, acooling member positioned between said pump and said container to beevacuated and adapted to transfer the heat in said container to saidcooler and located in the path of the vapor molecules, and a heattransferring element connecting said cooling member and said cooler, thethermal conductivity of said heat transferring element being of a valuesuch that said cooling member is maintained at a predeterminedtemperature level higher than said cooler and such that the vapor of thepump liquid contacting said cooling member condenses thereon, and aheating device being provided adjacent to said cooling member tomaintain said cooling member at the predetermined temperature higherthan said cooler temperature.

References Cited in the file of this patent UNITED STATES PATENTS(Addition to 765,978)

